Conventional assembly plants and assembly lines employed large conveyor systems to move components, partially assembled structures and assembly tooling/fixtures along an assembly line through sequential stations. These floor-mounted conveyors included powered rollers or belts which engaged and moved large, heavy pallets along an assembly path of travel. One example of a powered pallet transfer system is the VERSAPALLET® powered transfer system disclosed in U.S. Pat. No. 6,966,427 owned by the present assignee and incorporated herein by reference. These powered pallet systems have evolved to precisely and accurately position the pallets and supported components in modern assembly and manufacturing workstations and processes. One example of a powered pallet transfer system is the VERSACODER® powered transfer system disclosed in U.S. Pat. No. 7,108,189 owned by the present assignee and incorporated herein by reference. Examples of overhead conveyor systems, including devices for lowering components and subassemblies supported by the overhead conveyor downward into fixtures for processing, are described in one or more of U.S. Pat. Nos. 6,719,122; 6,557,690; 6,564,440; and 6,799,673 all of which are incorporated herein by reference.
These conventional assembly or transfer devices included large, heavy infrastructure, for example floor-mounted rail structures which supported the pallets carrying the partially assembled components. In addition to the large, heavy infrastructure, a disadvantage of floor-mounted or overhead conveyor systems is that the pallets or component supporting/holding fixtures are confined to the fixed path of travel of the conveyor, making it difficult to remove or insert a pallet or fixture.
More modern assembly plants increasingly use automated guided vehicles (AGV's) or automated guided carts (AGC's) to move components and equipment around assembly facilities. AGV's generally include sophisticated guidance devices, for example laser scanners, proximity sensors, GPS and the devices to guide the AGV along a predetermined course. AGV's are generally more accurate in following a preprogrammed path or course and stopping at a predetermined location, for example +/−ten (10) millimeters (mm), from a target position. As a result of the AGV's increased maneuverability and accuracy, AGV's are expensive. AGC's and other devices are less accurate in their maneuverability and accuracy, but are considerably less expensive than AGV's.
Even with the increased accuracy of AGV's (+/−10 mm), modern AGV's are still not accurate enough to use for positioning components and partially-assembled structures for modern precision assembly workstations or assembly cell operations. In addition, the use of AGV's were largely limited to moving components and equipment from one position to a predetermined destination. At the destination, a transfer of the partially-assembled component from the AGV to a fixture or other device directly used for the assembly process was needed. In such instances, a manipulator, for example by a robot, was required which requires additional infrastructure, floor space, time used to transfer, and increases costs to produce the final saleable product.
It would be advantageous to employ the use of AGVs, or AGV-like autonomous devices, to directly position components at workstations without use of large infrastructure-intensive devices like conventional pallet conveyors. It would be further advantageous to accurately and precisely locate components at workstations without auxiliary, or dedicated, equipment and methods such as powered manipulator devices such as programmable robots and/or supplemental positioning devices.